JP2002100397A - Cylindrical alkaline secondary cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an alkaline secondary cell with a high capacity which allows for preventing an insulation failure caused by a positive electrode containing an electroconductive substrate of a three dimensional structure. SOLUTION: In the alkaline secondary cell which is provided with an alkaline electrolyte and an electrode group 2 formed by winding with the positive electrode 3 and negative electrode 4 containing an electroconductive substrate of a three dimensional through the separator, he electrodes in a spiral, a sub- separator 6 having a liquid retention of 150% or more is arranged at least on the surface of a separator located between a initial winding edge part 3a of the electrode 3 and the electrode 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a cylindrical alkaline secondary battery having an improved separator.

[0002]

2. Description of the Related Art As alkaline secondary batteries, nickel cadmium secondary batteries and nickel hydrogen secondary batteries are known. Due to the increasing demand for high-capacity batteries due to the recent spread of PCs (personal computers) and mobile phones, and environmental issues, nickel-metal hydride secondary batteries have become mainstream as alkaline secondary batteries. Nickel-metal hydride secondary batteries are generally known as batteries having a cylindrical structure and batteries having a rectangular structure.

[0003] Cylindrical nickel-metal hydride secondary batteries include, for example,
A positive electrode having a structure in which a paste containing nickel hydroxide is filled in a three-dimensional conductive substrate such as an alkali-resistant metal porous body, and a two-dimensional conductive material such as a punched metal is used as a paste containing a hydrogen storage alloy. An electrode group is produced by spirally winding a separator (for example, composed mainly of a nonwoven fabric made of polyolefin) between a negative electrode having a structure filled in a conductive substrate and the electrode group, It is manufactured by storing an alkaline electrolyte in a container and closing the opening of the container. FIG. 4 is a sectional view showing the vicinity of the center of the electrode group. As shown in FIG. 4, the winding start portion of the negative electrode 21 and the winding start portion of the positive electrode 22, and the winding start portion of the positive electrode 22 and the negative electrode 21 in the second turn are separated by a single separator 23.

However, in the positive electrode including the above-described conductive substrate having a three-dimensional structure, a beard-like metal called burr is easily generated at an end of the positive electrode. In addition, when the electrode group is manufactured, the winding start portion of the positive electrode is wound with the smallest bending radius, so that cracks are easily generated. Therefore, the cylindrical nickel-metal hydride secondary battery has a burr at the winding start end of the positive electrode,
Cracks generated at the beginning of winding of the positive electrode during the production of the electrode group are likely to penetrate the separator, so that there is a problem that the rate of occurrence of insulation failure is high.

[0005] This insulation failure has become more frequent with the increase in capacity of nickel-metal hydride secondary batteries. In other words, in order to increase the capacity of a nickel-metal hydride secondary battery,
It is necessary to increase the capacity of the electrode group housed in the container, that is, to increase the capacity of the positive electrode and the negative electrode. Simply increasing the volume means increasing the thickness of the positive and negative electrodes. If the thickness is excessively increased, it becomes impossible to store the electrode group in the container.Thus, the thickness of the separator or the conductive substrate is reduced, or the diameter of the core used when manufacturing the electrode group is reduced. Take measures such as thinning. These measures tend to promote the incidence of insulation failure.

In view of the above, Japanese Patent Application No. Hei 10-284 is disclosed.
No. 209 proposes fixing a sub-separator having a shorter length than this separator to the main separator disposed outside the winding start portion of the positive electrode.

[0007]

However, since no attention has been paid to the electrolytic solution holding performance of the sub-separator, a high discharge capacity cannot be obtained.

The present invention is to provide a cylindrical alkaline secondary battery having a high capacity, in which insulation failure caused by a positive electrode including a conductive substrate having a three-dimensional structure is prevented.

[0009]

SUMMARY OF THE INVENTION A cylindrical alkaline secondary battery according to the present invention comprises an electrode group in which a positive electrode including a conductive substrate having a three-dimensional structure and a negative electrode are spirally wound via a separator, and an alkaline electrolyte. In the cylindrical alkaline secondary battery comprising: the secondary separator having a liquid retention of 150% or more is disposed at least on the separator surface existing between the winding start end of the positive electrode and the negative electrode. Is what you do.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION A cylindrical alkaline secondary battery according to the present invention comprises an electrode group in which a positive electrode and a negative electrode each including a conductive substrate having a three-dimensional structure are spirally wound via a separator, and an alkaline electrolyte. And a container in which the electrode group and the alkaline electrolyte are stored. The sub-separator having a liquid retention of 150% or more is disposed at least on the separator surface existing between the winding start end of the positive electrode and the negative electrode. Here, the winding start end of the positive electrode is 3 times the length of the positive electrode from the tip.
Means up to%.

Next, the positive electrode, negative electrode, separator (main separator), sub-separator and alkaline electrolyte will be described.

1) Positive Electrode This positive electrode has a structure in which a positive electrode material containing nickel hydroxide particles as an active material, a conductive material and a binder is supported on a conductive substrate having a three-dimensional structure.

As the nickel hydroxide particles, for example, single nickel hydroxide particles or nickel hydroxide particles in which a metal such as zinc, cobalt, bismuth or copper is coprecipitated with metallic nickel can be used. In particular, the latter positive electrode containing nickel hydroxide particles can further improve the charging efficiency in a high-temperature state.

Examples of the conductive material include cobalt oxides such as metallic cobalt, cobalt trioxide (Co ₂ O ₃ ) and cobalt monoxide (CoO), and cobalt hydroxide (C
and cobalt hydroxide such as o (OH) ₂ ).

Examples of the binder include hydrophobic polymers such as polytetrafluoroethylene (PTFE), polyethylene, and styrene-butadiene rubber (SBR); carboxymethylcellulose (CMC); methylcellulose;
C), hydrophilic polymers such as sodium polyacrylate (SPA) and polyvinyl alcohol (PVA). As the binder, two or three or more selected from the above-mentioned polymers can be used. The polytetrafluoroethylene can be used in the form of a dispersion.

As the conductive substrate having the three-dimensional structure, for example, a conductive substrate having a sponge-like, fiber-like, or felt-like porous structure formed of nickel, stainless steel, or a resin plated with nickel is used. Can be mentioned.

This positive electrode is prepared by adding a conductive material to, for example, nickel hydroxide particles as an active material, kneading it with a binder and water to prepare a paste, and filling the paste into a conductive substrate having a three-dimensional structure. Then, after drying, it is produced by pressure molding.

2) Negative Electrode The negative electrode has a structure in which a negative electrode material containing a hydrogen storage alloy, a conductive material and a binder is filled in a conductive substrate.

As the hydrogen storage alloy, for example, La
Ni _5, MmNi ₅ (Mm is misch metal), LmN
i ₅ (Lm is a La-enriched misch metal), and a multi-element alloy in which a part of Ni of these alloys is substituted by at least Al and Mn. The above-described multi-element hydrogen storage alloy has Al and Mn as substitution elements for Ni.
In addition, at least one element selected from Co, Ti, Cu, Zn, Zr, Cr and B may be included.
Above all, the general formula _{LnNi w Co x Al y Mn z} ( However, Ln is a rare earth element, the atomic ratio w, x, y, z respectively 3.30 ≦ w ≦ 4.50,0.50 ≦ x ≦ 1.10 ,
0.20 ≦ y ≦ 0.50, 0.05 ≦ z ≦ 0.20,
And the total value is 4.90 ≦ w + x + y + z ≦ 5.50
Is preferably used.

As the conductive material, for example, carbon black, graphite and the like can be used.

As the binder, at least one selected from the same types as those described for the positive electrode can be used.

Examples of the conductive substrate include a two-dimensional substrate such as a punched metal, an expanded metal, and a wire mesh, and a three-dimensional substrate such as a felt-like porous metal and a sponge-like porous metal.

The negative electrode may be, for example, the following (1):
It can be manufactured by the method described in (2).

(1) A conductive material is added to the powder of the hydrogen storage alloy and kneaded with a binder and water to prepare a paste. The paste is filled in a conductive substrate, dried, and then dried.
It is manufactured by press molding.

(2) A conductive material and a binder are added to the powder of the hydrogen storage alloy, kneaded to form a sheet, and the obtained sheet is laminated on a conductive substrate.

As the negative electrode, a sintered hydrogen storage alloy negative electrode can be used in place of the above-mentioned paste type hydrogen storage alloy negative electrode or dry type hydrogen storage alloy negative electrode.

3) Separator (Main Separator) This separator is, for example, a nonwoven fabric made of polyamide fiber,
It can be formed from a nonwoven fabric made of polyolefin fiber such as polyethylene or polypropylene, or a nonwoven fabric provided with a hydrophilic functional group. As a method for providing a hydrophilic functional group, for example, graft polymerization of a vinyl monomer, corona discharge treatment, and plasma treatment can be employed.

The liquid retention rate of the separator is 100 to 30.
It is preferable to be within the range of 0%. This is due to the following reasons. The liquid retention rate of the separator is 10
If it is less than 0%, it may be difficult to obtain a high discharge capacity. On the other hand, if the liquid retention exceeds 300%, the electrolyte held by the positive electrode is likely to move to the separator, so that swelling of the positive electrode is promoted and a long life may not be obtained. A more preferable range of the liquid retention rate is 150 to 3
00%.

The fibers constituting the separator preferably have an average diameter of 0.1 to 18 μm. A more preferred range is 3 to 10 μm.

The thickness of the separator ranges from 0.10 to 0.1.
Preferably, it is 20 mm.

The basis weight of the separator is 40 to 60 g.
/ M ² .

4) Sub-separator The sub-separator can be formed from, for example, a nonwoven fabric made of polyamide fiber, a nonwoven fabric made of polyolefin fiber such as polyethylene or polypropylene, or a nonwoven fabric provided with a hydrophilic functional group. As a method for providing a hydrophilic functional group, the same method as described for the separator can be used.

The liquid retention of the sub-separator is preferably set to 150% or more. This is due to the following reasons. If the liquid retention of the sub-separator is less than 150%, the amount of electrolyte held in the sub-separator becomes insufficient, and the sub-separator becomes a resistance component, so that the discharge capacity is reduced. Although the discharge capacity is improved as the liquid retention rate increases, when the liquid retention rate exceeds 400%, the electrolyte of the positive electrode easily moves to the separator, so that swelling of the positive electrode is promoted and a long life cannot be obtained. There is fear. A more preferable range of the liquid retention rate is 150 to 250%.

The length of the sub-separator is preferably in the range of 1 to 15% of the length of the main separator.

The fibers constituting the sub-separator preferably have an average diameter of 0.1 to 18 μm. A more preferred range is 3 to 10 μm.

The thickness of the sub-separator is preferably smaller than that of the main separator, and is preferably 0.20 mm or less. A more preferable range of the thickness of the sub-separator is 0.
15 ± 0.05 mm.

The basis weight of the sub-separator is from 20 to 60.
g / m ² is preferred.

The sub-separator may be fixed to the positive electrode side or the negative electrode side of the separator. In particular, it is preferable to fix to the negative electrode side. When fixed to the negative electrode surface side, it is possible to prevent the sub-separator from peeling off from the separator when producing the spiral electrode group.

The liquid retention ratio of the separator and the sub-separator is
It is measured by the method described below. 50 mm long and 50 m wide from the separator and sub-separator, respectively
A test piece having a thickness of 0.15 mm is cut out at m. After measuring the weight (W ₀ ) of each test piece, it is immersed in a 30% KOH aqueous solution for 2 minutes. Next, each test piece is taken out and left for 2 minutes, and then the weight (W ₁ ) of the test piece is measured, and the liquid retention rate is calculated by the following equation (1).

Liquid retention rate (%) = {(W ₁ −W ₀ ) / W ₀ } × 100 (1) As a method for fixing the separator and the sub-separator, for example, ultrasonic fusion, heat fusion, etc. Can be adopted. Among them, ultrasonic fusion is desirable.

5) Alkaline Electrolyte As the alkaline electrolyte, for example, a mixed solution of sodium hydroxide (NaOH) and lithium hydroxide (LiOH),
A mixture of potassium hydroxide (KOH) and LiOH, KOH
And a mixed solution of LiOH and NaOH.

Hereinafter, an example of a cylindrical alkaline secondary battery according to the present invention will be described with reference to FIGS.

FIG. 1 is a partially cutaway perspective view showing an example of a cylindrical alkaline secondary battery according to the present invention, and FIG. 2 is a sectional view showing the vicinity of the center of the electrode group in FIG.

An electrode group 2 is housed in a bottomed cylindrical container 1. The electrode group 2 is manufactured by spirally winding a positive electrode 3 and a negative electrode 4 with a separator (main separator) 5 having a sub-separator 6 fixed therebetween. In the electrode group 2, the positive electrode 3 is
(The winding direction is the backward direction). The sub-separator 6, which is shorter in length than the main separator 5, is fixed to the negative electrode side of the main separator 5 existing between the portion including the winding start end 3 a of the positive electrode 3 and the negative electrode 4. The front end of the sub-separator 6 precedes the winding start end 3a of the positive electrode (the winding direction is set to the rear). However, the winding start end 3a of the positive electrode 3 is 3 mm of the positive electrode length from the front end on the winding start side.
%.

On the other hand, the negative electrode 4 is arranged at the outermost periphery of the electrode group 2 and is in electrical contact with the container 1. The alkaline electrolyte is contained in the container 1. A circular sealing plate 8 having a hole 7 in the center is arranged at the upper opening of the container 1. Ring-shaped insulating gasket 9
Is disposed between the peripheral edge of the sealing plate 8 and the inner surface of the upper opening of the container 1. And airtightly fixed. The positive electrode lead 10
One end is connected to the positive electrode 2 and the other end is connected to the lower surface of the sealing plate 8. The hat-shaped positive electrode terminal 11 is mounted on the sealing plate 8 so as to cover the hole 7. A rubber safety valve 12 is disposed in a space surrounded by the sealing plate 8 and the positive electrode terminal 11 so as to close the hole 7. A circular holding plate 13 made of an insulating material having a hole in the center is arranged on the positive electrode terminal 11 such that a projection of the positive terminal 11 projects from the hole of the holding plate 13. The outer tube 14 is provided with the holding plate 13.
, The side surface of the container 1 and the bottom peripheral edge of the container 1.

With the configuration shown in FIGS. 1 and 2, burrs may be present at the winding start end of the positive electrode 3, or at the winding start end of the positive electrode 3 during fabrication of the electrode group 2. When cracks occur and new burrs occur,
Since the sub-separator 6 serves as a barrier against these burrs and can prevent the burrs from reaching the negative electrode 4, the rate of occurrence of insulation failure can be reduced. Also,
By fixing the sub-separator 6 on the side of the negative electrode of the main separator 5, the sub-separator 6 can be prevented from peeling off from the main separator 5 during the production of the electrode group 2.

In FIGS. 1 and 2 described above, the auxiliary separator is fixed to the separator present between the vicinity of the winding start end of the positive electrode and the negative electrode. May be fixed to the separator covering the. An example of this is shown in FIG.

That is, the main separator 5 present at the center of the electrode group 2 has an S-shape. The winding start end 3a of the positive electrode 3 exists in one bag of the S-shaped separator 5, and the front end surface 4a on the winding start side of the negative electrode 4 exists in the other bag. The sub-separator 15 is fixed to the negative electrode surface side of the S-shaped main separator 5 and the negative electrode surface side of the main separator 5 existing between the winding start end 3 a of the positive electrode 3 and the negative electrode 4.

With the configuration shown in FIG. 3, the burr existing at the winding start end 3a of the positive electrode 3 can be prevented from penetrating through the separator and coming into contact with the negative electrode 4. When a substrate having a two-dimensional structure such as punched metal is used as the conductive substrate, it is possible to suppress the burrs necessarily present on the front end face 4a of the negative electrode 4 from penetrating the separator. Therefore, the internal short circuit occurrence rate can be further reduced.

The above-described cylindrical alkaline secondary battery according to the present invention includes an electrode group in which a positive electrode including a conductive substrate having a three-dimensional structure and a negative electrode are spirally wound via a separator, and an alkaline electrolyte. . The sub-separator having a liquid retention of 150% or more is disposed at least on the separator surface existing between the winding start end of the positive electrode and the negative electrode.

According to such a secondary battery, since the sub-separator functions as a barrier against burrs existing at the winding start end of the positive electrode, it is possible to prevent the burrs of the positive electrode from coming into contact with the negative electrode through the separator. Can be. For this reason,
The internal short circuit occurrence rate can be reduced. Further, as a result of intensive studies conducted by the present inventors, even if the separator holds a sufficient amount of the alkaline electrolyte, if the electrolyte holding amount of the sub-separator is insufficient, the sub-separator becomes a resistance component. It was found that high capacity could not be obtained by working, and the internal resistance of the secondary battery could be reduced by increasing the liquid holding amount of the sub-separator to 150% or more, and thus it was clarified that high capacity could be obtained. .

Therefore, according to the present invention, a cylindrical alkaline secondary battery having a low internal short-circuit occurrence rate and a high capacity can be realized.

Further, the liquid holding ratio of the separator is 100 to
By setting the content within the range of 300%, the capacity and cycle life of the secondary battery can be further improved.

[0054]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to the drawings.

Example 1 <Preparation of Paste-Type Positive Electrode> A mixed powder composed of 90 parts by mass of nickel hydroxide powder and 10 parts by mass of cobalt monoxide powder was mixed with 0.25 parts by mass of carboxymethyl cellulose.
A paste was prepared by adding 0.25 parts by mass of sodium polyacrylate and 3.0 parts by mass of a dispersion of polytetrafluoroethylene (specific gravity 1.5, solid content 60% by weight) in terms of solid content and kneading. . Subsequently, the paste was filled into a nickel-plated fiber substrate as a conductive substrate having a three-dimensional structure, dried, rolled by roller pressing, and cut to produce a paste-type positive electrode.

<Preparation of Paste Type Negative Electrode> A commercially available lanthanum-enriched misch metal Lm and Ni, Co, Mn,
Al, LmNi _4.0 Co
_A hydrogen storage alloy having a composition of _0.4 Mn _0.3 Al _0.3 was produced. The hydrogen storage alloy is mechanically pulverized and
It was passed through a mesh sieve. Obtained hydrogen storage alloy 10
0.5 parts by mass of sodium polyacrylate, 0.125 parts by mass of carboxymethyl cellulose with respect to 0 parts by mass,
A paste was prepared by mixing 2.5 parts by mass of a dispersion of polytetrafluoroethylene (specific gravity 1.5, solid content 0.6% by weight) and 1.0 part by mass of carbon powder as a conductive material together with 50 parts by mass of water. Prepared. The obtained paste was applied to punched metal, dried, roll-formed, and cut to produce a paste-type negative electrode.

<Preparation of Main Separator> The liquid retention rate measured by the method described above is 230%, and the length is 96.0 mm.
With a thickness of 0.20 mm and a basis weight of 60.0 g / m
^{In 2} , a main separator made of a nonwoven fabric made of polypropylene fiber having an average fiber diameter of 10 μm and grafted with acrylic acid was prepared.

<Preparation of Sub-Separator> The liquid retention ratio measured by the method described above was 150%, the length was 20 mm (corresponding to 21% of the length of the main separator), and the thickness was 0.1%.
In 20 mm, basis weight at 50.0 g / m ^2, average fiber diameter acrylic acid was graft-polymerized were prepared sub separator made 10μm polypropylene fibers non-woven fabric.

<Fusion of Sub-Separator> A sub-separator was fused to the obtained main separator by ultrasonic waves so that the sub-separator was present between the start end of the positive electrode winding and the negative electrode. Obtained.

Next, the above-mentioned double separator was interposed between the above-mentioned negative electrode and the above-mentioned positive electrode, and spirally wound to produce an electrode group having the above-mentioned structure shown in FIG. In this electrode group, the sub-separator was disposed on the negative electrode side of the main separator existing between the positive electrode portion including the winding start end and the negative electrode.

After storing such an electrode group in a bottomed cylindrical container, 7 mol / m ³ of potassium hydroxide and 1 mol
1 / m ³ of lithium hydroxide containing an alkaline electrolyte and sealing it, etc., to form an AAA-sized cylindrical nickel-metal hydride secondary battery having the structure shown in FIG. 1 and a nominal capacity of 550 mAh. Was assembled.

(Examples 2 to 3 and Comparative Example 1) A cylindrical nickel-hydrogen secondary battery having the same structure as that of Example 1 except that the liquid retention rate of the sub-separator was changed as shown in Table 1 below. The battery was assembled.

(Comparative Example 2) Only the same main separator as described in Example 1 was interposed between the positive electrode and the negative electrode as described in Example 1 to form a spiral. The electrode group was produced by winding.

From the obtained electrode group, a cylindrical nickel-metal hydride secondary battery was assembled in the same manner as in Example 1 described above.

The obtained secondary batteries of Examples 1 to 3 and Comparative Examples 1 and 2 were charged at 0.2 CmA for 15 hours and then charged at 0.2 CmA until the battery voltage reached 1.0 V. The discharge capacity at the time of discharging was measured, and the results are shown in Table 1 below.

Further, with respect to the secondary batteries of Examples 1 to 3 and Comparative Examples 1 and 2, 10,000 electrode groups were prepared, and a voltage of 400 V was applied to each of the electrode groups housed in a container.
When a resistance value of MΩ was applied for 0.1 msec, the one that was energized was determined to be insulation failure, and the results are shown in Table 1 below.

[0067]

[Table 1]

As is clear from Table 1, Example 1 in which the secondary separator having a liquid retention of 150% or more was fixed to at least the main separator present between the winding start end of the positive electrode and the negative electrode.
It can be seen that the secondary batteries of Nos. 1 to 3 have a smaller number of insulation failures at the time of manufacture than the secondary battery of Comparative Example 2 and can obtain a discharge capacity almost equivalent to that of Comparative Example 2.

On the other hand, when the liquid retention rate of the sub-separator is 15
It can be seen that the discharge capacity of the secondary battery of Comparative Example 1, which is less than 0%, is lower than that of the secondary batteries of Examples 1 to 3.

[0070]

As described above in detail, according to the present invention, it is possible to provide a high-capacity alkaline secondary battery in which insulation failure due to a three-dimensionally structured conductive substrate included in the positive electrode is prevented. it can.

[Brief description of the drawings]

FIG. 1 is a partially cutaway perspective view showing an example of a cylindrical alkaline secondary battery according to the present invention.

FIG. 2 is a sectional view showing the vicinity of the center of the electrode group in FIG. 1;

FIG. 3 is a cross-sectional view showing another example of an electrode group incorporated in the cylindrical alkaline secondary battery according to the present invention.

FIG. 4 is a sectional view showing the vicinity of the center of an electrode group of a conventional alkaline secondary battery.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Container, 2 ... Electrode group, 3 ... Positive electrode, 3a ... Positive winding start end part 4 ... Negative electrode, 4a ... Front end surface of the negative winding start side 5 ... Main separator, 6 ... Secondary separator, 15 ... Secondary separator.

Claims (2)

[Claims] 1. A cylindrical alkaline secondary battery comprising an electrode group in which a positive electrode and a negative electrode each including a conductive substrate having a three-dimensional structure are spirally wound via a separator, and a cylindrical alkaline secondary battery having a liquid retention rate of 150 % Or more of the secondary separator is at least
A cylindrical alkaline secondary battery disposed on a surface of a separator present between a winding start end of a positive electrode and a negative electrode. 2. The liquid retention rate of the separator is 100 to 3
2. The cylindrical alkaline secondary battery according to claim 1, wherein the content is within the range of 00%.